1. Field of the Invention
The present invention relates to a vibration isolating apparatus which is interposed between a vibration generating portion and a vibration receiving portion so as to absorb and damp vibrations from the vibration generating portion.
2. Description of the Related Prior Art
One type of conventionally employed vibration isolating apparatus includes a hollow member of a resilient material which is filled with a liquid in such a manner as to enable it to be employed as a liquid chamber and which is partitioned into small liquid chambers through a limiting passage. This type of vibration isolating apparatus is arranged such that the liquid is caused to move between the two liquid chambers by the vibration acting on one of the chambers, whereby the vibration is absorbed by means of the fluid resistance of the liquid passing through the limiting passage.
The conventional vibration isolating apparatus of this type, however, suffers from the following problem. Namely, high-frequency vibrations easily cause the limiting passage to be clogged with the liquid, thus causing the dynamic scale factor to be undesirably increased, which fact involves a disadvantageously low capacity to absorb high-frequency vibrations. For this reason, employment of this type of vibration isolating apparatus as an engine mount may cause an occupant of the car in which it is employed to feel uncomfortable.
In order to overcome the above-described problem, a vibration isolating apparatus has heretofore been proposed in which the partition wall which divides the liquid chamber is provided with a vibrating plate which is capable of vibrating with very small amplitudes. In this conventional apparatus, the volume of each of the liquid chambers is variable by virtue of the action of the vibrating plate. Therefore, even after the limiting passage has been clogged at the time of generation of high-frequency vibrations, the dynamic to static ratio is favorably lowered due to the fact that the volume of the liquid chambers is conveniently varied by means of the vibrating plate.
However, even the apparatus having such a vibrating plate involves the disadvantage that, when a vibration of relatively large amplitude occurs, the dynamic to static ratio is increased and this causes the vibration absorbing characteristic to be undesirably lowered.